1. Field of the Invention
Rate-of-rotation sensors (gyroscopes) measure angular velocities or, generally, rotary movements. For measurement purposes, mechanical gyroscopes generally utilize the Coriolis force, in that a rotating mass body is deflected perpendicularly to the axis of rotation after the manner of a gyrocompass. In the process, an additional torque occurs about an axis perpendicular to these two axes of rotation, which leads to the precession movement known from gryroscopes. The strength of this additional torque is a measure of the rotational movement of the entire system.
In modern technology there is a growing need to detect movements in a detailed fashion, which also includes the measurement of the angular velocity. In the course of advancing miniaturization, in particular also in connection with the increasing use of electronic circuits, rate-of-rotation sensors are demanded which can be produced such that they are very small and in particular can be integrated with electronic components. Rate-of-rotation sensors produced using surface micromachining in semiconductor technology are therefore particularly suitable for a multiplicity of applications. One difficulty in the case of such micromechanical rate-of-rotation sensors resides in the fact that a complete rotational movement of a sensor element is not desirable or not possible, in a manner governed by the construction. Micromechanical rate-of-rotation sensors therefore usually contain mass parts which can be made to perform an oscillating rotary movement (rotary oscillation).
The publication by W. Geiger et al.: xe2x80x9cNew Designs of Micromachined Vibrating Rate Gyroscopes with Decoupled Oscillation Modesxe2x80x9d, in Proceedings IEEE Transducers 97, Chicago, June 1997, describes a rate-of-rotation sensor in which resilient torsional articulated joints are present between an inner part and an outer part of the movable mass. The intention is thus to compensate for or damp torques which act vertically with respect to the mass part and arise during the movement of the mass part because the resilient suspensions do not have a vertical axis of symmetry in their cross section, that is to say are parallelogram shaped, for example. This coupling between horizontal drive oscillation and vertical movement results, assuming isotropic elasticity properties, from a mixed planar moment of inertia of the suspension of the mass part with regard to the axes of movement of horizontal drive oscillation and vertical Coriolis movement. Therefore, it is necessary for the areas for detecting the Coriolis movement to be arranged and designed in such a way that vertical deflection of the suspension does not lead to a change in the detection signal. Moreover, as disclosed e.g. in the publication by R. Voss et al.: xe2x80x9cSilicon Angular Rate Sensor for Automotive Applications with Piezoelectric Drive and Piezoresistive Read-outxe2x80x9d in Proceedings IEEE Transducers 97, Chicago, June 1997, approximate correspondence between the resonant frequencies of the horizontal rotary oscillation and the vertical Coriolis oscillation to be detected is intended to be obtained.
DE 195 23895 A1 discloses a rate-of-rotation sensor having an oscillatory structure comprising two oscillating masses coupled rigidly to one another. The oscillatory structure is mounted on a substrate at a bearing point which coincides with the center of mass of the oscillatory structure. Situated below the oscillatory structure in the substrate are electrodes which capacitively detect the distance between the oscillatory structure and the substrate. Furthermore, a circuit arrangement is provided which, from the signal of the electrodes, determines a measure of the Coriolis acceleration acting on the rate-of-rotation sensor. This sensor has the disadvantage that if the oscillatory structure approaches the substrate to an excessive extent, the signal generated by the electrodes can lead to the circuit arrangement being overdriven.
The object of the present invention is to specify a mechanical resonator for rotation sensors which can be produced by micromachining and in which, even in the case of relatively large production tolerances, the measurement is not falsified by torques that additionally occur.
This object is achieved by means of the mechanical resonator having the features of claim 1. Refinements emerge from the dependent claims.
The resonator according to the invention comprises a mass part which functions as a centrifugal mass and is fixed by means of resilient suspension on a support. In the rest position of the mass part there exists an axis of symmetry with regard to which the mass part and the resilient suspension are mirror-symmetrical. The resilient suspension by which the mass part is fixed on a support is in the form of a strip and is aligned along said axis of symmetry. There are no suspensions which do not coincide with said axis of symmetry in the rest position of the mass part. The resonator is provided for detecting a rotary movement about an axis running perpendicularly to said axis of symmetry. The additional rotary oscillation which is excited on account of the Coriolis force is then effected about the axis of symmetry. Therefore, outside this axis of symmetry, the mass part is provided with electrically conductive areas as electrodes for detecting deflection of the mass part out of the plane of the rest position, which are assigned corresponding counterelectrodes lying opposite on the support. The electrode areas are preferably designed in such a way that during a rotary oscillation of the activated resonator, the form of the areas in which the electrodes overlap one another always remains the same. In the rest position, these overlap areas are preferably mirror-symmetrical with regard to the axis about which a rotary movement to be detected is effected. Negative feedback electrodes on the support are furthermore arranged opposite the electrode areas in the perpendicular direction. The negative feedback electrodes are arranged and dimensioned in such a way that by applying electrical potentials to the negative feedback electrodes, it is possible to compensate for a torque acting on the mass part about the straight line along which the resilient suspension is aligned.